To make or separate tweeters and low frequencies, just simply add a speaker/horns (best if they are not air able) and add a bipolar capacitor between cable and positive terminal of speaker/tweeter, better results if this speaker its a tweeter as such or least one closed speaker.
This placed in parallel to normal speaker, no matter is not showing or not at front, and voila, you now have a clearer sound! less opaque.

The capacitors to be used must be bipolar, for the tweeter's must be between 4uF and 12uF, for middle's from 10uF to 25uF. The circuitry for woofers / low is different.
If you cannot get a bipolar capacitor, simply its two capacitors join/together in a common pole, usually the negative pole. In this case two 4,5uF capacitors joined in common pole are same as 9uF bipolar capacitor.